Process for finishing the surfaces of bonded asbestos and the like and resulting product



' J. C. M ILDOWlE v v PROCESS FOR FINISHING THE SURFACES OF BONDED ASBESTOS AND THE LIKE AND RESULTING PRODUCT Filed March 24, 1925 vfim (707270 63 jiezcI 26201069, 9 /5 WMv-W 4 W5.

' Patented 11, 1928.

UNITED STATES g 1,695,253 PATENT OFFICE.

JOHN c. mcmnowm, or nnsmm, NEW rmmrsnnin, asslenonmo AsBEs'ros woon &; SHINGLE oo.,. oi NASEUA, new nmrsnmn, A CORPORATION or new nmr- SHIBE.

PROCESS IFOIR, FINISHING THE SURFACES OF BONDED ASBESTOS AND RESULTING PRODUCT.

THE LIKE AND Application filed ltarch 24, 1925. Serial No. 17,951.

The present invention relates to a process for providing a finished, polishedsurface upon cement bonded fibrous-materials, such as asbestos board and "the like, and to the product resulting from the operation of the process.

It is well known that materials, which are composed of comminuted material bonded l with hydraulic or other cement, usually pos- 10 sess a dull, rough, surface and that it is quite impossible without the application of some varnish-like substances to impart any luster thereto or even make it smooth. Moreover the surfaces of such materials are ordinarily porous, and persist in this condition, and

. unless coated with some impregnating fluid such as paint, there is no practicable or convenient'method of making it dense orrepellent, for example, to the penetration and re tention of moisture and other finely divided substances such as dust. But in man cases, fluid coatings may be quite undesira 1e, es-

:pecially when the specific qualities of the material itself are of particular importance, and

usually the fluid or semi-fluid binders which may be used do not permanently retain a high P011811. 1

As representative ofthis general category of materials, asbestos'board may be cited as so an example. This product is, used largely for the construction of electrical switchboards or the like, where high voltages are employed and where thddielmiic strength and other electrical'a-nd physic roperties of both the 85 surface and the body po ion of each element are of ci'itical importance. Hence, painting or otherwisefp oating the sur e is 'entlrely inappropriate, while at the samc time the presentation of a porous surface to the ab- 40 sorption of atmospheric moisture may be equally hazardous as well as unsatlsfactory on account of the accumulation of dust and dirt, not easily removed. l

. It is an object of this invention to provide (5 a process for imparting a finished, polished surface to bondedmaterials, such as bonded asbestos without altering the composition of either the surface or body portions thereof. and without deleteriously affecting the desirable physical characteristics such as electrical resistance, refractorinessychemical inertness,'strength, etc., which it may possess.

In its general aspect, the invention consists in a process whereby the interstices between particles at and near the surface of such material are filled and densely packed with very finely comminuted particles of substance" identical with that of which'the material is composed, while atthe same time the close- .grainedsurface thus formed is polished and rendered substantially continuous and impervious, as evidenced by the direct reflection of light therefrom, as from a mirror.

Preferably these two objects will be simultaneously achieved by converting superficial portions of the bonded material into the finely dividedfil'ling material, by grinding and polishing with a liquid, e. g. water or oil, which acts as a lubricant and also as a vehicle for distributingthe comminuted filling material and carrying it into the interstices of the body under the operations, which will preferably -be continued until the liquid vehicle has substantially disappeared.

A preferred and typical application of the invention will be described n its adaptation to the surfacing of-bonded asbestos board, and with reference to the accompanying drawings, in which-- Fig. 1- is a diagrammatic representation of an appropriate sandpapering device;

Fig. 2 is a side view of a sheet of asbestos board and of the polishing wheel in positionthereon for operation; a

Fig. 3 is a plan-view'of a segmental wheel;

Fig. 4 is an enlarged cross section of an unfinished sheet of asbestos; and p Fig. 5 is an enlarged cross'section of a finished sheet.

Referring to Fig. 1, the'sandpaperingdevice of sander-consists of a pairof arms 1, adapted to hold sheets of-sand paper 2 on the-under surfacethereof and mountedin a frame or casing 3 for transverse motion toward and away from each other under the f -mutual actuation ;of springs 4 and a cam 5, V which may be rotated by a small electrio motor, not shown, or other suitable means. -A handle 6 is provided for manual control of the device while in use.

The polishing wheel, as shown in Operation upon thesheet 10 (Fig. 2) comprises a universally mounted supporting arm 7 in the end of which is mounted a vertical counterpoised sleeve 8 provided with a' handle 13 and 1 position by support 16 in the frame .17.

Referring to Fig. 4, an exaggerated cross section of sheet 10 is shown as it appears before treating in accordance with the invention, presenting a rough surface 18 and projecting fibrous ends 19. Fig. 5 illustrates the character of the sheet after treatment, showing the consolidated surface portion 20 and the smooth level surface 21.

The asbestos board, for example such as made in accordance with the process described by Gharle's L. Norton, in Patent No. 929,004, issued July 27, 1909, which is representative of the procedure commonly employed, forthis purpose, is composed of shredded asbestos fibres which are mixed with a finely divided cementitious substance such as Portland cement and water. The mixture is made up to a convenient consistency and pressed into molds of the desired shape, (usually relatively thick sheets) under heavy hydraulic pressure, provision being made for the'uniform escape of water from the various portions'of the'inold. The sheet, as thus formed may be repressed and, after keeping it moist for a suitable "period to permit an incipient setting of the bond to take place,

it is allowed to dry, or is dried by direct contact with a current of dry, hot air or the like. While the foregoing treatment obviously may be varied, an essential ingredient is that the bonding element, of whatever nature it may consist, shall be set to a suiiicient degree to retain the granular or fibrous element,

namely the asbestos and any other material which may be incorporated therewith, firmly embedded therein and also to acquire a fair degree of rigidity in its own structural make up, thus presenting a relatively hard and uniform surface, though not altogether even and somewhat porous and dull as to color.

The sheet as thus obtained is placed upon a firm bed such as the support 16, and most conveniently, in a horizontalv position with the surface to be treated uppermost.

'place that which surface a part penetrating the pore spaces 7,

andpart remaining fun'absorbed, an amount sufiicient, for example, to make the surface glisten.

lVithout permitting prolonged absorption, the wheel 12 is started to rotateand then lowered gently, by manipulation of 'the' handle 13, into flat contact with the wet surand handle13. Meanwhile, additional water.

is permitted to drip upon the surface to reis absorbed by the sheet or evaporated. t q

A small proportion of the surface fibres is removed by this treatment which accumulates in small balls and is thrown off by the rotation of the wheel. But the removal of such, fibres is to be attributed to their extremely loose attachment to the sheet rather than to a tearingaction of the wheel, for there is no detachment of fibres sufliciently embedded to leave depressions or observable pits in the surface.

An emulsion or thick fluid'suspension composed of water and fine particles from the sheet' gradually forins, upon the continued action of the wheel, which is not' great in volume but which facilitates the continued operation of the process. The supply of additional water is next cut off, but the wheeling operation is, continued. The emulsion referred to is gradually consolidated with the surface of the sheet which loses its appearance of free moisture and develops a fine, dense, smooth surface. Upon continued operation this is transformed into a glossy sheen or highly polished reflecting surface of dense tions of the sander device which has'been described above. The surface'will be found sufficiently hard to resist any serious scratching, though if delayed the surface apparently acquires an additional hardening so that sanding of such places at a later time is difficult and not entirely satisfactory in the re- If large irregularities occur in the surface sults which maybe accomplished.

of the sheet to be finished, it is well not to depend upon removing them by the .subse quent operation, but to abrade them off by means of short quick passes of a sheet of fine emery paper over them. This is most eflec tively accomplished with-the sander device above described by passing it lightly ,or

heavily, as required, over the rough spots and reducing them to a relatively flat surface. A coatmg of water-is then applied to this absorption or retentionof moisture and is obnmate "face has been thus imparted to the sheet or other shape of the bonded material, no foreign substance has been added'thereto either on the surface or in the interstices.

Neither have the projecting points been merely removed and polished, leavin pits and hollows therebetween as ordinarily occurs when such substances are finished by other processes, but the whole surface is metamorphosed and consolidated and amal gamated into a continuous and homogeneous plane, the variations of which are comparable only to the wave lengths of light, as demonstrated by the fact that such" surfaces reflect ,clearly defined images, a result not hitherto ,those ordinarily bonded a rasives are entirely satisfacto and dense of structure and attainable upon materials of this character by anytreatment of which I am aware.

its flat surfaces exposed for application to the work, is preferably smooth, fine grained degree of hardness. A natural stone, such as used for making hones may ed, but it is found that artificiaflly or this purpose. For example, electrically used -alumina, crushed to pass a screen having 200 meshes to the linear 1nch, mixed with shellac, molded and heated to a suflicient temperature to soften and coalesce the mass into an integral structure, upon cooling and hardening produces a wheel of suitable structure, hardness, and uniformity both as to surface and as to the modifications which it undergoes during use.

it is aiso noteworthy that, in the final stage, or lishing operation of the process, the

be emplo san er may have its sand paper surface substitute'd by a sheet of flexible steel. For exerably of low viscosity ample'a saw blade has been successively em- 1ng passed over; the-already polished surface inthe same manner as when sand paper-is employed. may be done with or' without the addition of a small quantity of oil, (prefand surface tension) as desired. Ineither case the polished surface is additionally burnished, yielding an especially high degree of lustre or gloss. The oil also tends to mcrease the already dense surface roduced by the preceding treatment, if used, ut it is not essential to the desirable results of this operation.

' While the invention has been described in its specific application to the finishing of asbestos board, such as that prepared foruse in switch boards and the like, 1t will be clear possessed of a high layer of the same, metamorphose that it may also be conducted upon various other *materials, that may be chosen by analogy of composition or construction or other-comparable characteristics, and that the steps and degree of the procedure may be modified accordingly. It is also probable that the described results may be obtained by applying a finely divided mixture of constituents of the sheet to the surface to be treated, derived from an extraneous source instead of fromthat naturally occurring in the surface itself during the operation of the process.-

Such other adaptations and modifications of the invention, however, are to be understood as comprehended by the present disclosure and in the following claims.

I claim:

i 1. A bonded material comprising asbestos and a cementitious bond having a consolidated outer layer-of the same reduced to a substantially light'reflective surface- "2. -A,bon'ded material comprising asbestos anda cementitious-bond, having an outer layer ofthe same consolidated in situ and The wheel, alluded to above is of the seg-- mental type and adapted to be mounted with a bounded by a substantially planar surface.

3. A bonded material comprising asbestos and a cementitious bond having an outer layer consolidated in situ and bounded by a substantially planar surface, and a thin coating of oil thereon.

' 4. A bonded material comprising asbestos and a cementitious bond, having in situ to a more dense and consolidated structurethan the body portion. t. 5. A bonded material comprising asbestos and a cementitious bond, having an outer layer of the, same composition, consolidated in situ and bounded by asubstantially planar surface, said surface having the character-- istic property of reflecting light.

6; A method of finishing thev surface of cement-bonded asbestos material, which comprises filling and packing the interstices between the particles at or n'ear said surface with very finely comminuted particles, identical in composition with the cement-bonded asbestos surface, and polishing the close grained surface thus produced. I

7. A method of finishing the surface of cement-bonded asbestos'material, which comprises grinding the same with a liquid vehicle, thereby converting the superficial portions of the surface material into a finely divided filling material, compacting the filling material into the interstices between the par-, ticles of cement-bonded asbestos at and near the surface and polishing the thus consolidated surface material.

8. A method of finishing the surface of surface material into a finely divided'filling" an outer in cement-bonded asbestos material, which comicle, t ereby' I material, compacting tlie filling material into the interstices between the particles of ce-. ment-bonded asbestos at and near the surface, reducing the thus consolidated surface'mate- -rial to a plane surface, and continuing the operation until the liquid vehicle is absorbed and a light reflecting gloss is produced.

9. A method of preparing polished surfaces of cement-bonded asbestos, which comprises molding a wet mixture of an hydraulic cement and asbestos fiber into the desired shape, permitting the cementitious bond to partially set and, while the bond still retains some of its inherent capacity to set, filling and packing the interstices between the particles at and near the surface with finely comminuted particles substantially identical in composition and integral with the cementbonded asbestos surface, and polishing the close grained surface thus produced.

10. A method of preparing polished surfaces of cement-bonded asbestos,'which com prises molding a wet mixture of an hydraulic cement and asbestos fiber into" the desired shape, permitting the cementitious bond to;

partially set and, while the bond still retains some ofits inherent capacity to set, filling J composition and integral wit the'cement bonded asbestos surface, polishing the close grained surface thus produced and finally effecting complete and integral setting of the entire bonded mass.

11. A cement-bonded asbestos article, characterized by containing asbestos fibers bonded together by cement, the interstices between the particles at or near the surface of said article being packed with a finely divided filling substance identical in composition with the cement bonded portion of the article and integrally united therewith, the composite surface of said cement-bonded particles and said filling substance being characterized by a light reflective polish; t v

Signed by me at Nashua, N, 11., this nineteenth day ofMarch, 1925.

JOHN G. MAQILDOWIE. 

